Hydrocarbon desulfurization process

ABSTRACT

A process for the production of low sulfur hydrocarbonaceous products. The hydrocarbonaceous feedstock containing sulfur compounds is separated into a first hydrocarbonaceous stream containing the most refractory sulfur compounds and a second hydrocarbonaceous stream containing the least refractory sulfur compounds. The first stream desulfurized in a first desulfurization zone and the effluent along with the second hydrocarbonaceous stream is introduced into a second desulfurization zone.

BACKGROUND OF THE INVENTION

The field of art to which this invention pertains is desulfurization of a hydrocarbon feedstock to low levels of sulfur. Hydrodesulfurization processes have been used by petroleum refiners to produce more valuable hydrocarbonaceous streams such as naphtha, gasoline, kerosene and diesel, for example, having lower concentrations of sulfur and nitrogen. Feedstocks most often subjected to hydrotreating or desulfurization are normally liquid hydrocarbonaceous streams such as naphtha, kerosene, diesel, gas oil, vacuum gas oil (VGO) and reduced crude, for example. Traditionally, hydrodesulfurization severity is selected to produce an improvement sufficient to produce a marketable product. Over the years, it has been recognized that due to environmental concerns and newly enacted rules and regulations, saleable products must meet lower and lower limits on contaminants such as sulfur and nitrogen. Recently new regulations were proposed in the United States and Europe which basically require the complete removal of sulfur from liquid hydrocarbons which are used as transportation fuels such as gasoline and diesel.

Desulfurization is generally accomplished by contacting the hydrocarbonaceous feedstock in a desulfurization reaction vessel or zone with a suitable desulfurization catalyst under conditions of elevated temperature and pressure in the presence of hydrogen to yield a product containing the desired maximum limits of sulfur. The operating conditions and the desulfurization catalysts within the desulfurization reactor influence the quality of the desulfurized products.

It is known that during the desulfurization of a hydrocarbon stream as the severity of the desulfurization conditions is increased, the level of residual sulfur containing hydrocarbons decreases. This is due to the fact that certain sulfur compounds are more susceptible to the desulfurization reaction with the catalyst at given reaction conditions than are others. Not wishing to be bound by any theory, it is believed that the location of the sulfur atom in the compound determines if the sulfur atom will be more readily reacted with a catalytic site. If the sulfur atom is sterically hindered, i.e., having reduced access to the catalytic site, more severe reaction conditions must be employed in order to react and remove the sulfur atom from the hydrocarbonaceous compound. An example of a difficult to desulfurize or refractory compound is 4,6-dimethyl dibenzothiopene which has a boiling of 340° C. (636° F.).

Although a wide variety of process flow schemes, operating conditions and catalysts have been used in commercial desulfurization activities, there is always a demand for new desulfurization methods which provide lower costs and the required product quality. With the mandated low sulfur transportation fuels, the process of the present invention greatly improves the economic benefits of producing low sulfur fuels.

INFORMATION DISCLOSURE

U.S. Pat. No. 5,114,562 B1 (Haun et al) discloses a process wherein middle distillate petroleum streams are hydrotreated to produce a low sulfur and low aromatic product in two reaction zones in series. The effluent of the first reaction zone is purged of hydrogen sulfide by hydrogen stripping and then reheated by indirect heat exchange. The second reaction zone employs a sulfur-sensitive noble metal hydrogenation catalyst.

JP 04046993 A discloses the desulfurization of a hydrocarbon stream by firstly fractionating the hydrocarbon into two or more fractions and the resulting fractions are desulfurized individually and subsequently mixed together. The reference recognizes that the higher boiling fraction contains sulfur compounds that are difficult to decompose while the lower boiling fraction contains those compounds that are easier to decompose.

BRIEF SUMMARY OF THE INVENTION

The present invention is an improved process for the production of low sulfur hydrocarbonaceous products. It has been recognized that certain hydrocarbon boiling ranges are more easily desulfurized than other boiling ranges. Therefore, based on this information, the process of the present invention is able to more easily and economically desulfurize a hydrocarbonaceous feedstock. In accordance with the present invention, a hydrocarbonaceous feedstock containing sulfur compounds is separated into a first hydrocarbonaceous stream containing the most refractory sulfur compounds and a second hydrocarbonaceous stream containing the least refractory sulfur compounds. The first hydrocarbonaceous stream containing the most refractory sulfur compounds is desulfurized in a first desulfurization zone and the effluent therefrom along with the second hydrocarbonaceous stream containing the least refractory sulfur compounds is introduced into a second desulfurization zone. This permits the selection and use of the most suitable desulfurization catalysts and operating conditions to achieve ultra low residual sulfur in the hydrocarbon product stream.

In accordance with one embodiment, the present invention relates to a process to produce a low sulfur hydrocarbon stream from a sulfur containing hydrocarbonaceous feedstock wherein the process comprises the steps of: (a) separating the feedstock into a first stream containing more refractory sulfur compounds and a second stream containing less refractory sulfur compounds; (b) introducing the first stream containing more refractory sulfur compounds and hydrogen into a first hydrodesulfurization zone containing desulfurization catalyst to produce a first hydrodesulfurization zone effluent stream; (c) introducing at least a portion of the first hydrodesulfurization zone effluent stream, hydrogen and the second stream containing less refractory sulfur compounds into a second hydrodesulfurization zone containing hydrodesulfurization catalyst to produce a second hydrodesulfurization zone effluent; and (d) separating the second hydrodesulfurization zone effluent to produce a low sulfur hydrocarbon product stream.

In accordance with another embodiment, the present invention is a process to produce an ultra low sulfur diesel stream from a sulfur containing hydrocarbonaceous feedstock boiling in the range of diesel fuel wherein the process comprises the steps of: (a) separating the feedstock into a first stream containing more refractory sulfur compounds and a second stream containing less refractory sulfur compounds; (b) introducing the first stream containing more refractory sulfur compounds and hydrogen into a first hydrodesulfurization zone containing desulfurization catalyst to produce a first hydrodesulfurization zone effluent stream; (c) introducing at least a portion of the first hydrodesulfurization zone effluent stream, hydrogen and the second stream containing less refractory sulfur compounds into a second hydrodesulfurization zone containing hydrodesulfurization catalyst to produce a second hydrodesulfurization zone effluent; and (d) separating the second hydrodesulfurization zone effluent to produce an ultra low sulfur diesel stream containing less than about 50 wppm sulfur.

In another embodiment, the present invention is a process to produce an ultra low sulfur diesel stream from a sulfur containing hydrocarbonaceous feedstock boiling in the range of diesel fuel wherein the process comprises the steps of: (a) separating the feedstock into a first stream containing more refractory sulfur compounds and in an amount less than about 30 volume percent of the feedstock and a second stream containing less refractory sulfur compounds; (b) introducing the first stream containing more refractory sulfur compounds and hydrogen into a first hydrodesulfurization zone containing desulfurization catalyst at operating conditions including a temperature from about 204° C. (400° F.) to about 482° C. (900° F.), a pressure from about 2.1 MPa (300 psig) to about 17.3 MPa (2500 psig) and a liquid hourly space velocity from about 0.1 hr⁻¹ to about 10 hr⁻¹ to produce a first hydrodesulfurization zone effluent stream; (c) introducing at least a portion of the first hydrodesulfurization zone effluent stream, hydrogen and the second stream containing less refractory sulfur compounds into a second hydrodesulfurization zone containing hydrodesulfurization catalyst at operating conditions less severe than those in the first hydrodesulfurization zone and including a temperature from about 204° C. (400° F.) to about 482° C. (900° F.), a pressure from about 2.1 MPa (300 psig) to about 17.3 MPa (2500 psig) and a liquid hourly space velocity from about 0.1 hr⁻¹ to about 10 hr⁻¹ to produce a second hydrodesulfurization zone effluent; and (d) separating the second hydrodesulfurization zone effluent to produce an ultra low sulfur diesel stream containing less than about 50 wppm sulfur.

Other embodiments of the present invention encompass further details such as types and descriptions of feedstocks, desulfurization catalysts and preferred operating conditions including temperatures and pressures, all of which are hereinafter disclosed in the following discussion of each of these facets of the invention.

BRIEF DESCRIPTION OF THE DRAWING

The drawing is a simplified process flow diagram of a preferred embodiment of the present invention. The drawing is intended to be schematically illustrative of the present invention and not be a limitation thereof.

DETAILED DESCRIPTION OF THE INVENTION

It has been discovered that a more efficient and economical production of ultra low sulfur hydrocarbon products including ultra low sulfur diesel stock can be achieved and enjoyed in the above-described integrated hydrodesulfurization process.

Although the present invention is particularly useful for the production of ultra low sulfur diesel, any suitable hydrocarbonaceous feedstock may be used in the present invention. Illustrative hydrocarbon feedstocks include naphtha and kerosene and those containing components boiling above 288° C. (550° F.), such as atmospheric gas oils, vacuum gas oils, deasphalted vacuum and atmospheric residua, mildly cracked residual oils, cracked gas oils, coker distillates, straight run distillates, solvent-deasphalted oils, pyrolysis-derived oils, high boiling synthetic oils, cycle oils and cat cracker distillates. A preferred feedstock is a gas oil or other hydrocarbon fraction having at least about 50% by weight, and most usually at least about 75% by weight of its components boiling at a temperature between about 315° C. (600° F.) and 538° C. (1000° F.).

The selected feedstock is separated by fractionation or any other convenient method to produce a first hydrocarbonaceous stream containing more refractory sulfur compounds and a second stream containing less refractory sulfur compounds. The first stream containing more refractory sulfur compounds preferably comprises less than about 30 volume percent of the hydrocarbonaceous feedstock. Hydrocarbonaceous sulfur compounds are graded according to the difficulty in removing sulfur from the hydrocarbonaceous sulfur compounds. Certain hydrocarbonaceous compounds due to their physical characteristics are more resistant to desulfurization than other hydrocarbonaceous compounds having different characteristics. Therefore, the hydrocarbonaceous sulfur compounds, which are more difficult to desulfurize, are considered to be refractory. In many cases, the higher boiling hydrocarbonaceous sulfur compounds are found to be more refractory than the lower boiling hydrocarbonaceous sulfur compounds. In the case of diesel boiling range hydrocarbons, the higher boiling hydrocarbons are more refractory to desulfurization. The separation of diesel boiling range hydrocarbons for the present invention is conveniently performed in a splitter or a fractionation zone.

In accordance with the present invention, the first hydrocarbonaceous stream containing more refractory sulfur compounds is introduced along with hydrogen into a desulfurization zone containing desulfurization catalyst and operated at desulfurization conditions. Preferred desulfurization conditions include a temperature from about 204° C. (400° F.) to about 482° C. (900° F.) and a liquid hourly space velocity of the hydrocarbonaceous feed from about 0.1 hr⁻¹ to about 10 hr⁻¹.

Suitable desulfurization catalysts for use in the present invention are any known conventional hydrotreating catalysts and include those which are comprised of at least one Group VIII metal, preferably iron, cobalt and nickel, more preferably cobalt and/or nickel and at least one Group VI metal, preferably molybdenum and tungsten, on a high surface area support material, preferably alumina. Other suitable desulfurization catalysts include zeolitic catalysts, as well as noble metal catalysts where the noble metal is selected from palladium and platinum. It is within the scope of the present invention that more than one type of desulfurization catalyst be used in the same reaction vessel. The Group VIII metal is typically present in an amount ranging from about 2 to about 20 weight percent, preferably from about 4 to about 12 weight percent. The Group VI metal will typically be present in an amount ranging from about 1 to about 25 weight percent, preferably from about 2 to about 25 weight percent. Typical desulfurization temperatures range from about 204° C. (400° F.) to about 482° C. (900° F.) with pressures from about 2.1 MPa (300 psig) to about 17.3 MPa (2500 psig), preferably from about 2.1 MPa (300 psig) to about 13.9 MPa (2000 psig).

The resulting effluent from the first desulfurization zone is introduced into the second desulfurization zone along with hydrogen the second stream containing less refractory sulfur compounds. The second desulfurization zone contains desulfurization catalyst which may be the same or different from the desulfurization catalyst used in the first desulfurization zone and may be selected from any known desulfurization catalyst such as those described hereinabove for example. Preferred desulfurization conditions may be selected from those ranges taught for the first desulfurization zone and may be more, less or equal to the severity of reaction conditions selected for the first desulfurization zone.

The resulting effluent from the second desulfurization zone is partially condensed and introduced into a vapor-liquid separator operated at a temperature from about 21° C. (70° F.) to about 60° C. (140° F.) to produce a hydrogen-rich gaseous stream containing hydrogen sulfide and a liquid hydrocarbonaceous stream. The resulting hydrogen-rich gaseous steam is preferably passed through an acid gas scrubbing zone to reduce the concentration of hydrogen sulfide to produce a purified hydrogen-rich gaseous stream, a portion of which may then be recycled to either one or both of the desulfurization zones. The liquid hydrocarbonaceous stream is preferably introduced into a cold flash drum to remove dissolved hydrogen and normally gaseous hydrocarbons and subsequently sent to a fractionation zone. It is preferred that the low sulfur hydrocarbon product stream contains less than about 50 wppm sulfur, more preferably 10 wppm sulfur. The make-up hydrogen may be introduced into the process at any convenient location, but in a preferred embodiment, the make-up hydrogen is introduced into the first desulfurization zone.

DETAILED DESCRIPTION OF THE DRAWING

In the drawing, the process of the present invention is illustrated by means of a simplified schematic flow diagram in which such details as pumps, instrumentation, heat-exchange and heat-recovery circuits, compressors and similar hardware have been deleted as being non-essential to an understanding of the techniques involved. The use of such miscellaneous equipment is well within the purview of one skilled in the art.

With reference now to the drawing, a feed stream comprising a heavy diesel boiling range distillate fraction enters the process through line 1 and is introduced into fractionation zone 2. A hydrocarbonaceous stream containing the more refractory sulfur compounds is removed from the bottom of fractionation zone 2 via line 4 and is introduced into desulfurization zone 8 via line 7 along with a make-up hydrogen stream which is introduced via lines 6 and 7, and a hydrogen-rich gaseous stream provided via lines 18 and 7. Another hydrocarbonaceous stream containing less refractory sulfur compounds is removed from fractionation zone 2 via line 3 and is introduced via line 3 into heat-exchanger 13 and the resulting heated effluent is transported via lines 5 and 10 and is introduced into desulfurization zone 11 along with the effluent from desulfurization zone 8 which is carried via lines 9 and 10. The resulting effluent from desulfurization zone 11 is transported via line 12 and introduced into heat-exchanger 13 and the resulting cooled stream is carried via line 14 and introduced into heat-exchanger 15. The resulting partially condensed stream from heat-exchanger 15 is carried via line 16 and introduced into high-pressure separator 17. A hydrogen-rich gaseous stream is removed from high-pressure separator 17 via line 18 and recycled as described hereinabove. A liquid hydrocarbonaceous stream having low concentrations of sulfur compounds is removed from high-pressure separator 17 via line 19 and recovered.

The process of the present invention is further demonstrated by the following illustrative embodiment. This illustrative embodiment is, however, not presented to unduly limit the process of this invention, but to further illustrate the advantage of the hereinabove-described embodiment. The following data were not obtained by the actual performance of the present invention but are considered prospective and reasonably illustrative of the expected performance of the invention.

ILLUSTRATIVE EMBODIMENT

A distillate feedstock having the characteristics presented in Table 1 is hydrodesulfurized in accordance with the prior art in a single stage reaction zone utilizing a commercially available hydrodesulfurization catalyst operated at the conditions presented in Table 3 under “Prior Art” to produce a 149° C.+diesel product having a residual sulfur level of 5 wppm. The product yields from the desulfurization reactor are presented in Table 4.

Another portion of the feedstock having the characteristics presented in Table 1 is separated by fractionation into two fractions as presented in Table 2. The heavier fraction containing essentially all of the refractory sulfur compounds is hydrodesulfurized in a first reaction zone utilizing the same type of commercially available hydrodesulfurization catalyst and the resulting effluent is introduced into a second hydrodesulfurization reaction zone along with the lighter fraction to produce a reactor yield presented in Table 4. The reaction zone conditions are presented in Table 3 under “Invention” and a 149° C.+diesel product having a residual sulfur level of 5 wppm is produced.

From Table 3, it can be seen that the present invention requires only 78% of the catalyst in the prior art process which means that less catalyst is required to perform the same level of desulfurization shown in Tables 4 and 5 and the reactor volume is less as well. Since the recycle gas rate for the present invention is only 50% of the prior art rate, the recycle gas circuit equipment is smaller while maintaining comparable yields and product qualities with the same catalyst cycle length. These overall results translate to lower investment and operating costs for a desulfurization unit to produce ultra low sulfur product. TABLE 1 Distillate Feedstock Analysis 20% Straight Run Distillate 40% Light Coker Gas Oil 40% Light Cycle Oil Distillation, ° C. (° F.) Initial Boiling Point 180 (356) 10 226 (439) 30 261 (501) 50 285 (545) 70 311 (592) 90 346 (656) 95 364 (687) End Point 376 (709) Sulfur, weight percent 1.31 Nitrogen, weight ppm 1100

TABLE 2 Separated Feedstock Lighter Fraction Heavier Fraction Volume Percent 75 25 Sulfur, weight percent 1.16 1.75 Nitrogen, weight ppm 700 2200 Refractory Sulfur Trace 4x Feed Concentration Distillation, ° C. (° F.) Initial Boiling Point 180 (355) 310 (590) 50% 271 (520) 343 (650) End Point 321 (610) 376 (710)

TABLE 3 Comparison of Operating Conditions Prior Art Invention Pressure, kPa (psig) 6650 (950) 6650 (950) Catalyst Volume Base 0.78 Base Recycle Gas Rate Base  0.5 Base Reactor Temperature  360 (680) <357 (675) Requirement, ° C. (° F.)

TABLE 4 Comparison of Desulfurization Reactor Yields Prior Art Invention Base Base Hydrogen Consumption Weight Percent of Feedstock Hydrogen Sulfide 1.39 1.39 Ammonia 0.13 0.13 C₁-C₄ 0.37 0.37 C₅-149° C. 4.09 4.09 149° C.+ 95.70 95.70

TABLE 5 Comparison of Product Quality 149° C. + Diesel Prior Art Invention Sulfur, weight ppm 5 5 Nitrogen, weight ppm 1 1

The foregoing description, drawing and illustrative embodiment clearly illustrate the advantages encompassed by the process of the present invention and the benefits to be afforded with the use thereof. 

1-15. (canceled)
 16. A process to produce an ultra low sulfur diesel stream from a sulfur containing hydrocarbonaceous feedstock boiling in the range of diesel fuel wherein the process comprises the steps of: (a) separating the feedstock into a first stream containing more refractory sulfur compounds and in an amount less than about 30 volume percent of the feedstock and a second stream containing less refractory sulfur compounds; (b) introducing the first stream containing more refractory sulfur compounds and hydrogen into a first hydrodesulfurization zone containing desulfurization catalyst at operating conditions including a temperature from about 204° C. (400° F.) to about 482° C. (900° F.), a pressure from about 2.1 MPa (300 psig) to about 17.3 MPa (2500 psig) and a liquid hourly space velocity from about 0.1 hr⁻¹ to about 10 hr⁻¹ to produce a first hydrodesulfurization zone effluent stream; (c) introducing at least a portion of the first hydrodesulfurization zone effluent stream, hydrogen and the second stream containing less refractory sulfur compounds into a second hydrodesulfurizalion zone containing hydrodesulfurization catalyst at operating conditions less severe than those in the first hydrodesulfurization zone and including a temperature from about 204° C. (400° F.) to about 482° C. (900° F.), a pressure from about 2.1 MPa (300 psig) to about 17.3 MPa (2500 psig) and a liquid hourly space velocity from about 0.1 hr⁻¹ to about 10 hr⁻¹ to produce a second hydrodesulfurization zone effluent; and (d) separating the second hydrodesulfurization zone effluent to produce an ultra low sulfur diesel stream containing less than about 50 wppm sulfur.
 17. The process of claim 16 wherein the ultra low sulfur diesel stream contains less than about 10 wppm sulfur. 